The use of antistatic agents to prevent buildup of static charges on polymeric surfaces is well known. As is so often the case, the use of these materials requires a compromise between competing effects. For instance, an effective concentration on the surface of an article can make that surface sticky. Also some of the best antistatic agents are what is known as "internal" agents, that is, agents which are designed to be compounded into the resin as opposed to being coated onto the surface of the finished article. These agents generally do not produce an immediate effect, but rather require as much as three days or more to migrate to the surface. In addition, having the antistatic agent in the polymer during compounding and extrusion frequently causes color problems.
It is known to apply an antistatic agent by coating the inside of a mold in a conventional blow molding operation as is shown in Boeke, U.S. Pat. No. 3,400,116 (1968).
There has recently been developed a technique for producing biaxially oriented hollow articles such as bottles from reheated parison preforms. These preforms are produced by extruding a continuous length of tubing which is cut into individual lengths. It has been found that prior art techniques for eliminating static charges are not entirely satisfactory with these biaxially oriented articles. For instance, if the coating is applied to the molten extrudate immediately upon extrusion, prior to entering the sizing sleeve, much of the material is lost in the water bath which is conventionally used downstream from such a sizing sleeve. If the material is applied to the finished parison, it has been found that the agent does not adhere well enough and can be easily removed by abrasion partly because of the presence of lubricant generally employed during the sizing of the tubing and also because the agent is only loosely held on the surface of the parison. If the antistatic agent is incorporated into the polymer, there is the normal problem of color formation during compounding and extrusion and the additional problem of static buildup during the time the parisons are reheated and formed into the final product.